Cars zoom by on the boulevards overhead as work progresses on expanding the subway underneath -- and in between a full-fledged Roman city has emerged right in the heart of the Bulgarian capital.

Archaeologists have little by little unearthed well-preserved stretches of cobbled Roman streets, a public bath, the ruins of a dignitary's house and the curved wall of an early Christian basilica, all dating back to the 4th century AD.

If all goes well, the ruins will be fashioned into a vast underground museum due to open to the public in late 2012....